CAKKKINK PREPARATION 42. CH...N CO I Caffeine (Trimethyl xanthine), CO C N(CI 1,) CH...N C- N ,'yCI1 Digest the tea with 500 c.c. boiling water for a. quarter of an hour, and filter through cloth into a basin placed over a ring- burner (see p. 108), so that the liquid in the filter is kept hot. Moderately line unsized cotton cloth is used, and is wetted and stretched on a wooden frame as shown in Kig. '/S- Wash with a further 250 c.c. of boiling water. Add to the. iiltrate a, solu- tion of basic lead acetate (made by boiling acetate of lead solution with excess of litharge, and then filtering) until no more precipitate is formed. Killer hot through a large lluted filter froiM precipitated albumin, and wash with water. To thr boil • ing filtrate add dilute sulphuric acid until the le'id is precipitated as sulphate. Kilter or de-cant from the sulphate of le;ul, and concentrate the solution with the addition of animal charcoal to 250 300 c.c. Miter and extract the filtrate three times witb small quantities (50 c.c.) of chloroform. Distil off the chloro- form on the water-bath, and dissolve the residue in a. small quantity of hot water. On allowing (he solution to evaporate very slowly, long silky needles of caffeine separate, which may have a slightly yellow tint, in which case they should be drained, re-dissolved in water, and boiled with the addition of animal charcoal. The needles contain one molecule of water, which they lose at 100 and melt at 234*5". Meld about rf; grams. See Appendix, p. 269.